Electronic And Transport Properties Of Boron Nitride-Graphene Hybrid Nanostructures

With the successful preparation of advanced nanomaterials of carbon （C） andboron nitride （BN）, such as graphene, graphene nanoribbons （GNRs）, h-BN-sheets,boron nitride nanoibbons （BNNRs）, carbon nanotubes （CNTs） and boron nitridenanotubes （BNNTs）, and their potential applications in future nano-electronics, theseC-or BN-based nanomaterials become the research focus in condensed matter physics.The boron nitride-graphene hybrid nanostructures with unique structure, rich physicaland chemical properties, spin polarization properties and modulated electronic andtransport properties soon arouse people’s attention. In this thesis the structuralcharacteristics, electronic structures and transport properties of several typical boronnitride-graphene hybrid nanomaterials are systematically investigated. Somesignificant results are summarized as follows:1. We report the size limitation effct of the half-metallic properties in the hybridzigzag BNC nanoribbons using the density functional theory based first-principlesmethods. We find that all hybrid systems hold antiferromagnetic ground states.Systems holding ZGNR segments with fixed9zigzag carbon chains are metals notdepending on the variation of the ZBNNR segments. Transitions betweensemiconductor, half-metal and metal can be realized in both systems as the width ofthe carbon segment increases.2. The structures, stability and electronic properties of a series two-segmenthybrid nanotubes BN_20-nC_nNTs and some novel four-segment hybrid nanotubesBN_mC_mBN_mC_mNTs and BN_mC_mNB_mC_mNTs （m=3,4,5） are systematically investigatedusing the density functional theory in combination with non-equilibrium Green’sfunctions. We find that the two-segment nanotubes can be narrow band-gapsemiconductors depending on their chemical compositions. All four-segmentBN_mC_mNB_mC_mNTs are metals and all four-segment BN_mC_mBN_mC_mNTs aresemiconductors with band gaps decreasing as the increasing of their diameters.Further investigations on the transport properties of the pure C20NT, the two-segmentBN10C10NT and the four-segment BN₅C₅BN₅C₅NTs and BN₅C₅NB₅C₅NTs reveal thatthe two-segment hybrid manner could not improve the tube’s transport properties.However, an obvious transport enhancement is found in the four-segment nanotubes,especially in the metallic BN₅C₅NB₅C₅NTs where a6G₀transmission peak appears inits transport spectrum.3. The transport properties and differential conductance of the heterostructuresconstructed by single-wall carbon nanotube （SWCNT） and single-wall boron nitridenanotube （SWBNNT） are investigated using the density functional theory incombination with non-equilibrium Green’s functions. SWCNT（5,5） and SWBNNT （5,5） are taken as example. We find that the transmission conductance and differentialconductance of （5,5） BN/C nanotube heterostructure are continually depressed as theBNNT region increases.4. The electronic transport properties of hybrid graphene nanoribbons constructed by substituting C atom chain into B （N） atom chain are investigated using the densityfunctional theory in combination with the non-equilibrium Green’s functions. It isfound that the hybrid nanoribbon with armchair edge transits from semiconducting tometallic. While the transport properties of hybrid B （N） system with zigzag edge arehighly improved with the transmission conductance around the Fermi level increasingto6G₀（5G₀）.5. Based on the Anderson tight-binding model, the electronic properties ofdisordered bilayer hexagonal boron nitride quantum films are investigated. Ournumerical results show that the electrons in disordered bilayer hexagonal boronnitride quantum film are localized, presenting an insulating behavior. However, forthe monolayer disordered bilayer hexagonal boron nitride quantum film, the energyspectrum has persistent mobility edges which are independent of the disorder strength.This indicates that a metal-insulator transition occurs in the monolayer disorderstructure.